This invention relates to the art of extruded reclosable plastic fasteners of the kind in which complementary male and female profiles are capable of elastically engaging with one another for connecting opposed panels of sheet material such as the walls of bags made from the sheet material.
Reclosable fasteners of the kind identified are well known and widely used in sacks or bags made from plastic sheet or film material, for the packaging of numerous and varied products. The profiles have complementary generally hook-shaped connecting structure and by virtue of resilient flexibility are adapted to be digitally pressed together into interlocked condition and to be digitally separated by pulling them apart. Although the profiles may be integrally extruded with the plastic sheet or film material, they may also be separately extruded and attached to the material by fused welding, adhesive attachment, or the like.
More particularly, the invention is concerned with the type of fastener comprising male and female profiles wherein the female profile is composed of a base joined to the associated sheet and of two arms joined to this base and having opposed terminal jaws directed toward the base of the profile. These two jaws are intended to cooperate with two complementary lateral projections or barbs which comprise the head of the male profile in order for the latter to remain captured by the female profile after their mutual elastic engagement. Separation of the profiles is obtained by applying relatively differential separating forces to the sheets to which the profiles are attached, depending on whether the force is being applied from inside or outside the bag formed from the sheets. Such interlocking fastener means are well known and in wide usage, being particularly employed in order to close sacks or bags of plastic material which are presently employed, particularly in industry and commerce, for the sale of products of general use such as articles of clothing, small implements, food products which are frozen or not frozen, etc.
In current technology, it is customary, among other things, to assure the juncture between the female profile and the corresponding sheet by means of a relatively large seating surface in order to prevent this female profile from tilting during the operation of engagement with the male profile. At the discharge of the extruding die and during the forced cooling phase imposed on the sheet and on the female profile, however, this large seating surface acts like a veritable thermal bridge between the sheet and the female profile and thus lends itself to transfer of material by creep between the two elements.